System and method for reducing harmonic distortion

ABSTRACT

A method is disclosed including but not limited to supplying a voltage waveform from a higher power electrical bus to a lower power electrical bus; sensing on the lower power electrical bus, a deviation from a sinusoidal voltage waveform in the voltage waveform supplied from the higher power electrical bus; generating a correction current to adjust the deviation in the voltage on the lower power bus to a substantially sinusoidal voltage waveform; and filtering the correction current to substantially attenuate the correction current from propagating through the filter from the lower power electrical bus to the higher power electrical bus. A system is disclosed for performing the method.

CROSS REFERENCE TO RELATED APPLICATIONS

The patent application claims priority from U.S. Provisional PatentApplication Ser. No. 61/510,347 entitled “A System and Method forReducing Harmonic Distortion” by John Bradford Janik filed on Jul. 21,2011, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

Numerous applications provide high voltage power distribution busseswhich power electrical and electronic devices connected to the powerdistribution bus. Often times, electrical equipment acting as a load onthe high voltage power distribution bus introduce noise onto the highvoltage power distribution bus. In some cases, harmonic distortioncurrents are generated by the load on the high voltage powerdistribution bus. The harmonic distortion currents are problematic whenthey occur in an electrical circuit. In many of the these high voltagedistribution buses, step down electrical power transformers are providedto step down the higher voltage on the higher voltage power distributionbus to a lower voltage supplied to a lower voltage power distributionbus. Unfortunately the harmonic currents generate noise on the voltagesupplied from the high power voltage distribution bus, which are passedthrough the step down to the lower voltage power distribution bus. Insome cases, the noisy voltage passed down to the lower voltage is inappropriate for electrical components existing as a load on the lowervoltage power distribution bus. Thus, there is a need for a system andmethod for monitoring, filtering and cleaning up an electrical systeminto which harmonic distortion currents are injected.

FIELD OF THE DISCLOSURE

The present disclosure describes a system and method for reducingharmonic distortion in an electrical circuit.

SUMMARY OF THE DISCLOSURE

A method is disclosed including but not limited to supplying a voltagewaveform from a higher power electrical bus to a lower power electricalbus; sensing on the lower power electrical bus, a deviation from asinusoidal voltage waveform in the voltage waveform supplied from thehigher power electrical bus; generating a correction current to adjustthe deviation in the voltage on the lower power bus to a substantiallysinusoidal voltage waveform; and filtering the correction current tosubstantially attenuate the correction current from propagating throughthe filter from the lower power electrical bus to the higher powerelectrical bus. A system is disclosed for performing the method.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an operational environment for a particular illustrativeembodiment wherein an ocean going vessel is providing electrical powerto a tethered submarine;

FIG. 2 depicts a schematic representation of an apparatus provided in aglobal approach to harmonic distortion;

FIG. 3 depicts a schematic representation of an apparatus in accordancewith a particular illustrative embodiment; and

FIG. 4 depicts a flow chart of a particular illustrative embodiment of amethod.

DETAILED DESCRIPTION

Harmonic distortion from loads in an electrical system cause variationsin the power supplied to the electrical system. Thus, power variationsthat occur in a high power bus in the electrical system are transferredto lower power buses that receive power from the higher power electricalbus. In the past, many of these harmonic distortion problems thatoccurred in electrical power applications have been addressed byglobally by sensing harmonic distortion currents on the higher powerelectrical bus generated by a main load on the higher power bus in theelectrical system. Thus, in the past, some electrical engineers globallysolved local harmonic noise voltage problems with a global solutionapplied to the higher power electrical bus to solve a local harmonicdistortion power supply problems the were transferred to lower powerbus. In the past global approach, a current transformer was placed onthe higher power electrical bus near a main load which generatedharmonic distortion currents on the main high power electrical bus.

In the global approach, the current transformer was connected in reversepolarity to the main high power electrical bus near the main load on thehigher power electrical bus. Thus, the polarity of the harmonic currentsgenerated by the main load and sensed by the current transformer was areverse polarity to the harmonic anti-currents generated by the currenttransformer. The anti-currents generated by the current transformer werethen injected back to the main load to counter act and offset theharmonic distortion currents generated by and coming from the main loadon the higher power bus. This global approach generated harmonicanti-currents that mirrored harmonic currents generated by the load onthe higher voltage power distribution bus. Thus, this global solutionrequired higher rated components that could hand higher voltages andcurrents used in the higher voltage power distribution bus.

While this old global approach works for solving global electricalharmonic distortion problems on the higher voltage bus, the globalsolution can be an expensive over kill for solving a local harmonicdistortion voltage problem on a particular local lower power bus. Theglobal solution can also be prohibitively expensive to implement inorder to solve a local harmonic voltage problem on a local lower powersub section of the main high power section of the electrical bus. It isconsiderably cheaper to address the “noisy” voltage problems such as theharmonic distortion problem on the lower power electrical bus wherecurrent ratings and voltage ratings are reduced from the higher voltagesand current ratings of the higher voltage electrical bus. In some caseswhere the voltage and power are an order of magnitude higher on thehigher voltage bus, a cost savings of an order of magnitude or a factorof ten can be realized by solving the noisy voltage problem on the lowerpower electrical bus.

In the higher voltage “global” approach, harmonic currents generated bya noisy load on the higher voltage bus are sensed and harmonicanti-currents are generated to clean up the voltage on the main higherpower electrical bus, which in turn provides a cleaned up power to astep down transformer that supplies power to the lower power electricalbus. In “local” solution of a particular illustrative embodimentdescribed herein, lower power components are provided that sense noisyvariations in power supplied from the higher voltage to the lower powerelectrical bus. In contrast to the global approach where harmonicdistortion in the power supplied is caused by a load on the higher powerbus, in the local system and method described herein, the source of theharmonic distortion is the voltage supplied from the higher powerelectrical bus caused by the load on the higher power electrical bus.

Thus, in the local solution, the harmonic currents are flowing into thelocal load in contrast to the harmonic currents flowing from the load onthe higher power distribution bus. In addition, in the local solution,the noisy voltage sourced from the higher power bus is sensed andcorrected. In a particular illustrative embodiment, the local load issubstantially resistive and does not generate significant harmoniccurrents. Thus, in a particular illustrative embodiment, the voltagesupplied from the higher power bus is sensed and corrected. In the localsolution the resistive load does not produce substantial harmoniccurrents so that current transformers placed near the local load areplaced in phase with the current flowing to the local load. An activefilter senses the local voltage variations and generates currents tocorrect the voltage variations, thereby cleaning up a lower voltagepower supplied to electrical components on the local lower powerdistribution bus.

In one particular embodiment the higher voltage electrical power issupplied in an ocean going vessel electrical system. Variations in thehigher voltage power supplied are cleaned up locally on the lower powerbus. After cleaning up the lower power voltage at the local level on thelower power bus, the lower power electrical bus supplies cleaned uppower to a submarine tethered to the local lower power electrical busvia a 1500 meter power tether cable. The power is step up from 480 VACon the lower power electrical bus to 6000 VAC and supplied to thesubmarine power tether cable. The power is stepped up via an electricalpower transformer to reduce losses incurred in providing power to thesubmarine over a 1500 meter power cable. The stepping up of the powerform the lower power electrical bus also steps up voltage variations orpower spikes that occur on the local lower power electrical bus. Thesestepped up power spike can interfere with video and control signals thatappear on the submarine tether cable. These stepped up power spike canalso harm or burn out electrical device connected to the 6000 VAC powersupply tether. Thus, it becomes desirable to clean up the voltage on thelower power bus the local level before supplying power to the submarinetether at 6000 VAC.

In a particular illustrative embodiment, a system and method areprovided in which the local harmonic distortion problem on the lowerpower electrical bus is solved at the local level rather than applyingthe global approach of the past. Additionally, the local low voltageelectrical components are less expensive than global high voltageelectrical components. Thus, in a particular illustrative embodiment,the local solution helps to reduce cost, weight and volume of electricalsystem components on a ship.

In an illustrative embodiment, an active filter, which may consist of,but is not limited to a reactor is provided on a low side of atransformer between the higher power bus and the lower power bus sectionof an electrical system. The transformer is provided to step downvoltage between higher voltage electrical bus and the lower powerelectrical bus. The reactor includes but is not limited to an inductor.The inductor acts as a filter between the higher voltage electrical busand the lower power electrical bus. The inductor filter blocks localharmonic anti-currents generated in the lower power sub section of theelectrical system on the low side of the step down transformer to solvethe local harmonic voltage distortion generated in the lower powersubsection of the electrical system. In a preferred embodiment asubstantially resistive load is provided on the lower power electricalbus. The filter substantially attenuates the harmonic currents generatedin lower power electrical bus so that the currents are not transferredback into the higher power electrical bus.

In an illustrative embodiment, harmonic voltage variations on thevoltage supplied to the lower power electrical bus from the higher powerelectrical bus, are sensed and corrected. Typically the primary voltageon the higher power electrical bus is stepped down via an electricalpower transformer positioned between the higher power electrical bus andthe lower power electrical bus. In a particular embodiment, a harmonicdistortion voltage appears on the voltage signal supplied from thehigher power electrical bus to the lower power electrical bus.

In one particular example of an illustrative embodiment, harmonicvoltage variations are generated by and are sourced from a load on themain high power electrical bus in the ship borne electrical system. Theload on the higher power electrical bus can consist of but is notlimited to silicone controlled rectifiers, electrical motors which cangenerate substantial variations in the voltage level on the higher powerelectrical bus. In an illustrative embodiment, the local load is not thesource of harmonic voltage variations. In one particular illustrativeembodiment, harmonic voltage variations on the lower power electricalbus are reduced by sensing the harmonic voltage variations in thevoltage supplied from the higher power electrical bus. An active filtergenerates corrective currents to adjust the local voltage on lower powerelectrical bus without affecting the higher voltage on the highervoltage electrical bus. In a particular embodiment, a local currenttransformer is connected in a like polarity to the local lower powersubsection of the electrical bus near the local load. The filter (suchas a reactor, inductor or other electrical filter) between the main highpower electrical bus and the local lower power electrical bussubstantially attenuates the local corrective currents generated at theharmonic distortion frequencies so that these local harmonic correctivecurrents do not feed back into the higher electrical power bus.

In an illustrative embodiment, the local solution saves money by afactor of 10 over the cost of a global solution, based on a comparisonof the cost of an active electrical filter for the higher powerelectrical circuit and the less expensive lower power active filter onthe lower power electrical bus. Part of the savings is due to the lowercost of the lower power components compared to higher power componentsthat would be used on the higher power bus of the electrical system.

Turning now to FIG. 1, in a particular illustrative embodiment 100 a seagoing vessel 102 such as a ship contains an electrical power supplysystem 106 that generates and distributes power to electrical componentson the ship. The electrical components include but are not limited tolights, motors, and silicone controlled rectifiers. The electrical powersupply system also supplies power to a submarine 110 through anelectrical cable 108. In a particular illustrative embodiment, theelectrical cable is 1500 meters long. A schematic depiction of aparticular illustrative embodiment of the electrical power electricalsupply system is shown in FIG. 3.

Turning now to FIG. 2, FIG. 2 depicts a schematic representation 200 ofa system in accordance with a global solution to harmonic voltagedistortion the electrical power electrical supply system on the ship. Asshown in FIG. 2, in the global solution power is supplied fromelectrical generator 214 to a 600 VAC main higher power bus 202. Voltagevariations including but not limited to harmonic distortion on the 600VAC higher power bus 202 are induced by loads such as the siliconecontrolled rectifier DC drive 201 and reactor load 204. A higher poweractive filter 207 is applied to generate anti-currents to offsetharmonic currents sensed by a current transformer 209 attached to theelectrical bus near the loads 204 and 205. The active filter 207includes but is not limited to a processor in data communication with acomputer readable storage medium containing computer instructions thatwhen executed by the processor performs functions. The loads 204 and 205are symbolic and representative of loads that appear on a higher powerelectrical bus on a ship but are not all inclusive as the power supplyrequirements on a ship are diverse. The current transformer 209 isconnected in reverse polarity so that harmonic currents generated by theloads 204 and 205 that are sensed and generated by the currenttransformer are inverted. The inverted harmonic currents sensed by thecurrent transformer are fed to the AC active filter via cable 219. TheAC active filter then generates harmonic anti-currents 213 and injectsthe anti-currents onto the higher power electrical bus 202 whichsubstantially mirrors and cancels out the harmonic currents generated bythe loads 204 and 205. The components on the higher power electrical busincluding the active filter are rated for a higher power bus to at least600 VAC.

Turning now to FIG. 3, FIG. 3 depicts a particular illustrativeembodiment 300 of the present invention. As shown in FIG. 3, power issupplied from electrical generator 214 to a 600 VAC main higher powerbus 202. Voltage variations including but not limited to harmonicdistortion on the 600 VAC higher power bus 202 are induced by loads suchas the silicone controlled rectifier DC drive 201 and reactor load 204.Power is supplied from the higher voltage bus 202 to transformer 206which steps down the higher power 600 VAC the lower power 480 VACsupplied to the lower power bus 203. In a particular illustrativeembodiment, an active filter 212 is provided on the lower powerelectrical bus. One suitable active filter is commercially availablefrom ABB n.v. Power Quality Products, Avenue Centrale, 10, ZoningIndustriel de Jumet, B-6040 Charleroi (Jumet), Belgium Phone +32 71 250811. The active filter 212 includes but is not limited to a processor indata communication with a computer readable storage medium containingcomputer instructions that when executed by the processor performsfunctions.

In the illustrative embodiment depicted in FIG. 3, current transformers210 are connected so that the harmonic voltage deviations from asinusoidal wave form sensed on the lower power bus are corrected or“cleaned up” to appear more as a more sinusoidal waveform. In aparticular embodiment, deviations from a sinusoidal voltage wave form inthe stepped down voltage on the lower power bus are sensed and correctedby an active filter 212 and current transformers 210 so that the steppeddown lower voltage is “cleaned up” and appears more sinusoidal. In anillustrative embodiment, the current transformers 210 are connected nearthe loads 216 and 217. The current transformers are connected so thatcurrents sensed and generated by the current transformers are notinverted. Harmonic frequency distortion variations in the voltagesupplied from the higher power electrical bus 202 are sensed by thecurrent transformers 210. Active filter 212 generates harmonic frequencycorrective currents 213 to substantially reduce deviations from asinusoidal wave form in the voltage on the lower power bus. The activefilter injects the harmonic frequency corrective currents into the lowerpower electrical bus to clean up the voltage on lower power bus 203 tosupply a cleaned up substantially sinusoidal voltage wave form on thelower power bus 203. The lower power bus then supplies cleaned upsubstantially sinusoidal voltage to the load 216 which can be thesubmarine 110 on the end of a 1500 meter cable 108. Filter 208, whichcan be but is not limited to a reactor or inductor substantiallyattenuates the harmonic corrective currents generated by the activefilter 212. Thus, the corrective currents are substantially attenuatedby the filter 208. The filter 208 thus substantially blocks the harmoniccorrective currents generated on the lower power bus from transferringback to the higher power bus 202 and power generator 214.

Turning now to FIG. 4, FIG. 4 depicts a flow chart of an illustrativeembodiment 400 of a method in accordance with the present invention. Asshown in FIG. 4, a flow chart for a method is depicted for anillustrative embodiment of the method. As shown in block 402 an initialoptional step in the method is supplying a voltage waveform from ahigher power electrical bus to a lower power electrical bus. As shown inblock 404, the method performs sensing on the lower power electricalbus, a deviation from a sinusoidal voltage waveform in the voltagewaveform supplied from the higher power electrical bus. A shown in block406, the method performs generating a correction current and injectingthe correction current onto the lower power bus to adjust the deviationin the voltage on the lower power bus to a substantially sinusoidalvoltage waveform. A shown in block 408, the method performs filteringthe correction current to substantially attenuate the correction currentfrom propagating through the filter from the lower power electrical busto the higher power electrical bus.

In another illustrative embodiment, a method is disclosed including butnot limited to supplying a voltage waveform from a higher powerelectrical bus to a lower power electrical bus; sensing on the lowerpower electrical bus, a deviation from a sinusoidal voltage waveform inthe voltage waveform supplied from the higher power electrical bus;generating a correction current to adjust the deviation in the voltageon the lower power bus to a substantially sinusoidal voltage waveform;and filtering the correction current to substantially attenuate thecorrection current from propagating through the filter from the lowerpower electrical bus to the higher power electrical bus. In anotherembodiment of the method the deviation is at a harmonic frequency. Inanother embodiment of the method the filter substantially attenuates theharmonic frequency. In another embodiment of the method the sensing ofthe harmonic anti-current is at frequency higher than a fundamentalfrequency for the voltage supplied from the main high power electricalbus so that the filter attenuates the harmonic frequencies higher thanthe fundamental frequency.

In another embodiment a system is disclosed including but not limited toa higher power electrical bus; a transformer in electrical communicationwith the higher power electrical bus; a lower power electrical bus inelectrical communication with the transformer; a filter positionedbetween the transformer and the lower power electrical bus and inelectrical communication with the higher power electrical bus and thelower power electrical bus; a current transformer in electricalcommunication with the lower power electrical; an active filter inelectrical communication with the current transformer and the lowerpower electrical bus for a deviation from a sinusoidal voltage waveformon the lower power electrical bus; an active filter in electricalcommunication with the current transformer for generating a correctioncurrent to adjust the deviation in the voltage on the lower powerelectrical bus to a substantially sinusoidal voltage waveform on thelower power electrical bus; and a filter positioned between thetransformer and the lower power electrical bus for to substantiallyattenuate the correction current to substantially block the correctioncurrent from propagating through the filter from the lower powerelectrical bus to the higher power electrical bus. In another embodimentof the system, the deviation is at a harmonic frequency for thefundamental frequency of power supplied on the lower power electricalbus. In another embodiment of the system, the filter substantiallyattenuates the correction current at the harmonic frequency. In anotherembodiment of the system, the harmonic correction current is atfrequency higher than a fundamental frequency for the voltage suppliedfrom the main high power electrical bus so that the filter attenuatesthe harmonic correction current frequencies higher than the fundamentalfrequency.

While the non transitory computer readable medium is shown in an exampleembodiment to be a single medium, the term “computer readable medium”should be taken to include a single medium or multiple media (e.g., acentralized or distributed database, and/or associated caches andservers) that store the one or more sets of instructions. The term“computer readable medium” shall also be taken to include anynon-transitory medium that is capable of storing, encoding or carrying aset of instructions for execution by the machine and that cause themachine to perform any one or more of the methodologies of theillustrative embodiment. The term “computer readable medium” shallaccordingly be taken to include, but not be limited to: solid-statememories such as a memory card or other package that houses one or moreread-only (non-volatile) memories, random access memories, or otherre-writable (volatile) memories; magneto-optical or optical medium suchas a disk or tape; and/or a digital file attachment to e-mail or otherself-contained information archive or set of archives is considered adistribution medium equivalent to a tangible storage medium.Accordingly, the illustrative embodiment is considered to include anyone or more of a computer readable medium or a distribution medium, aslisted herein and including art-recognized equivalents and successormedia, in which the software implementations herein are stored.

The illustrations of embodiments described herein are intended toprovide a general understanding of the structure of various embodiments,and they are not intended to serve as a complete description of all theelements and features of apparatus and systems that might make use ofthe structures described herein. Many other embodiments will be apparentto those of skill in the art upon reviewing the above description. Otherembodiments may be utilized and derived there from, such that structuraland logical substitutions and changes may be made without departing fromthe scope of this disclosure. Figures are merely representational andmay not be drawn to scale. Certain proportions thereof may beexaggerated, while others may be minimized. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “illustrativeembodiment” merely for convenience and without intending to voluntarilylimit the scope of this application to any single invention or inventiveconcept if more than one is in fact disclosed. Thus, although specificembodiments have been illustrated and described herein, it should beappreciated that any arrangement calculated to achieve the same purposemay be substituted for the specific embodiments shown. This disclosureis intended to cover any and all adaptations or variations of variousembodiments. Combinations of the above embodiments, and otherembodiments not specifically described herein, will be apparent to thoseof skill in the art upon reviewing the above description.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment.

Although the illustrative embodiment has been described with referenceto several illustrative embodiments, it is understood that the wordsthat have been used are words of description and illustration, ratherthan words of limitation. Changes may be made within the purview of theappended claims, as presently stated and as amended, without departingfrom the scope and spirit of the illustrative embodiment in its aspects.Although the illustrative embodiment has been described with referenceto particular means, materials and embodiments, the invention is notintended to be limited to the particulars disclosed; rather, theinvention extends to all functionally equivalent structures, methods,and uses such as are within the scope of the appended claims.

In accordance with various embodiments of the present illustrativeembodiment, the methods described herein are intended for operation assoftware programs running on a computer processor. Dedicated hardwareimplementations including, but not limited to, application specificintegrated circuits, programmable logic arrays and other hardwaredevices can likewise be constructed to implement the methods describedherein. Furthermore, alternative software implementations including, butnot limited to, distributed processing or component/object distributedprocessing, parallel processing, or virtual machine processing can alsobe constructed to implement the methods described herein.

1. A method comprising: supplying a voltage waveform from a higher powerelectrical bus to a lower power electrical bus; sensing on the lowerpower electrical bus, a deviation from a sinusoidal voltage waveform inthe voltage waveform supplied from the higher power electrical bus;generating a correction current to adjust the deviation in the voltageon the lower power bus to a substantially sinusoidal voltage waveform;and filtering the correction current to substantially attenuate thecorrection current from propagating through the filter from the lowerpower electrical bus to the higher power electrical bus.
 2. The methodof claim 1, wherein the deviation is at a harmonic frequency.
 3. Themethod of claim 2, wherein the filter substantially attenuates theharmonic frequency.
 4. The method of claim 3, wherein the sensing of theharmonic anti-current is at frequency higher than a fundamentalfrequency for the voltage supplied from the main high power electricalbus so that the filter attenuates the harmonic frequencies higher thanthe fundamental frequency.
 5. A system comprising: a higher powerelectrical bus; a transformer in electrical communication with thehigher power electrical bus; a lower power electrical bus in electricalcommunication with the transformer; a filter positioned between thetransformer and the lower power electrical bus and in electricalcommunication with the higher power electrical bus and the lower powerelectrical bus; a current transformer in electrical communication withthe lower power electrical; an active filter in electrical communicationwith the current transformer and the lower power electrical bus for adeviation from a sinusoidal voltage waveform on the lower powerelectrical bus; an active filter in electrical communication with thecurrent transformer for generating a correction current to adjust thedeviation in the voltage on the lower power electrical bus to asubstantially sinusoidal voltage waveform on the lower power electricalbus; and a filter positioned between the transformer and the lower powerelectrical bus for to substantially attenuate the correction current tosubstantially block the correction current from propagating through thefilter from the lower power electrical bus to the higher powerelectrical bus.
 6. The system of claim 5, wherein the deviation is at aharmonic frequency for the fundamental frequency of power supplied onthe lower power electrical bus.
 7. The system of claim 6, wherein thefilter substantially attenuates the correction current at the harmonicfrequency.
 8. The system of claim 7, wherein the harmonic correctioncurrent is at frequency higher than a fundamental frequency for thevoltage supplied from the main high power electrical bus so that thefilter attenuates the harmonic correction current frequencies higherthan the fundamental frequency.